Wireless local area networks (WLANs), such as a wireless medium in a communication network using Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), are founded on the principles of collision avoidance. Such networks may also conform to a communication standard such as a communication protocol of 802.11 type e.g. Medium Access Control (MAC).
The IEEE 802.11 MAC standard defines the way WLANs must work at the physical and medium access control (MAC) level. Typically, the 802.11 MAC (Medium Access Control) operating mode implements the well-known Distributed Coordination Function (DCF) which relies on a contention-based mechanism based on the so-called “Carrier Sense Multiple Access with Collision Avoidance” (CSMA/CA) technique.
The 802.11 medium access protocol standard or operating mode is mainly directed to the management of communication nodes waiting for the medium to become idle so as to try to access to the medium.
The network operating mode defined by the IEEE 802.11ac standard provides very high throughput (VHT) by, among other means, moving from the 2.4 GHz band which is deemed to be highly susceptible to interference to the 5 GHz band, thereby allowing for wider frequency contiguous channels of 80 MHz, two of which may optionally be combined to get a 160 MHz channel as operating band of the wireless network. The 802.11ac standard also tweaks the Request-To-Send (RTS) and Clear-To-Send (CTS) frames to allow for composite channels of varying and predefined bandwidths of 20, 40 or 80 MHz, the composite channels being made of one or more contiguous sub-channels within the operating band. The 160 MHz composite channel is possible by the combination of two 80 MHz composite channels within the 160 MHz operating band.
A composite channel therefore consists of a primary channel and at least a secondary channel of for example 20 MHz each. The primary channel is used by the communication nodes to sense whether or not the channel is idle, which channel can thus be extended using the secondary channel to form a composite channel.
Tertiary and quaternary channels may also take part of the composite channel.
A station is allowed to use as much channel capacity (or bandwidth, i.e. of sub-channels in the composite channel) as is available. The constraint is that the combined channels need to be contiguous for a station with a single antenna station (or single spatial stream).
However, if there is noise or interference on one of the 20 MHz channel within the wider composite channel, the available bandwidth is reduced. The 802.11ac standard only allows a restricted number of composite channel configurations, i.e. of predefined subsets of 20 MHz channel that can be reserved by the 802.11ac stations to transmit data. These are contiguous channels of 20, 40, 80 MHz bandwidth in case of single antenna devices.
Therefore, noise or interference even on a small portion of the composite channel may substantially reduce the available bandwidth of the composite channel to only 40 or 20 MHz., since the resulting reserved bandwidth must meet the 20 MHz, 40 MHz, 80 MHz or 160 MHz channel configurations allowed by the standard.
More recently, Institute of Electrical and Electronics Engineers (IEEE) officially approved the 802.11ax task group, as the successor of 802.11ac. The primary goal of 802.11ax consists to improve data speed for devices used in dense deployment scenarios.
The huge gigabit throughputs that are often attributed to 802.11ac are mainly theoretical. In fact, they represent the overall capacity a Wi-Fi network can support, for instance 1.3 Gbps in today's most advanced routers. However, they can occur only in the rarest circumstances where any individual device would actually be able to connect at such high rates.
The existing 802.11ac standard requires that the composite channel width be specified in the 802.11ac frames, resulting in that channels non-contiguous within the operating band cannot be used although they are available. Therefore, in the 802.11ax research context, there is a need to enhance the efficiency and usage of the wireless channel.
Publication IEEE 802.11-13/1058r0 “Efficient Wider Bandwidth Operation” provided during the 802.11ax task group has raised the benefit of using all available channels, even if no solution to do so has been provided.